Plague is a serious bacterial infection that's transmitted by fleas. Known as the Black Death during medieval times, today plague occurs in fewer than 5,000 people a year worldwide. It can be deadly if not treated promptly with antibiotics.

The organism that causes plague, Yersinia pestis, lives in small rodents on every continent except Australia. The organism is transmitted to humans who are bitten by fleas that have fed on infected rodents or by humans handling infected animals.

The most common form of plague results in swollen and tender lymph nodes — called buboes — in the groin, armpits or neck. The rarest and deadliest form of plague affects the lungs, and it can be spread from person to person.

Plague is divided into three main types — bubonic, septicemic and pneumonic — depending on which part of your body is involved. Signs and symptoms vary depending on the type of plague.

Bubonic plague

Bubonic plague is the most common variety of the disease. It's named after the buboes — swollen lymph nodes — which typically develop within a week after an infected flea bites you. Buboes may be:

Blackening and death of tissue (gangrene) in your extremities, most commonly your fingers, toes and nose

Pneumonic plague

Pneumonic plague affects the lungs. It's the least common variety of plague but the most dangerous, because it can be spread from person to person via cough droplets. Signs and symptoms can begin within a few hours after infection, and may include:

Cough, with bloody sputum

Difficulty breathing

High fever

Nausea and vomiting

Weakness

Pneumonic plague progresses rapidly and may cause respiratory failure and shock within two days of infection. If antibiotic treatment isn't initiated within a day after signs and symptoms first appear, the infection is likely to be fatal.

When to see a doctor

Seek immediate medical attention if you begin to feel ill and have been in an area where plague has been known to occur. This includes parts of several states in the western portion of the United States — primarily New Mexico, Arizona and Colorado.

The plague bacteria, Yersinia pestis, is transmitted to humans when they are bitten by fleas that have previously fed on infected animals, such as:

Rats

Squirrels

Rabbits

Prairie dogs

Chipmunks

The bacteria can also enter your body if you have a break in your skin that comes into contact with an infected animal's blood. Domestic cats can become infected with plague from flea bites or from eating infected rodents.

Pneumonic plague, which affects the lungs, is spread by inhaling infectious droplets coughed into the air by a sick animal or person.

The risk of developing plaque is very low. Worldwide, only a few thousand people develop plague each year. However, your risk of plague can be increased by where you live and travel, your occupation, and even by some of your hobbies.

Location

Plague outbreaks are most common in rural areas and in urban areas characterized by overcrowding, poor sanitation and a high rat population. The greatest number of human plague infections occurs in Africa.

Occupation

Veterinarians and their assistants have a higher risk of coming into contact with domestic cats that may have become infected with plague. Also at higher risk are people who work outdoors in areas where plague-infested animals are common.

Hobbies

Camping, hunting or hiking in areas where plague-infected animals reside can increase your risk of being bitten by an infected flea.

Complications of plague may include:

Death. Most people who receive prompt antibiotic treatment survive bubonic plague. Untreated plague has a high fatality rate.

Gangrene. Blood clots in the tiny blood vessels of your fingers and toes can disrupt the flow of blood and cause that tissue to die. The portions of your fingers and toes that have died may need to be amputated.

If you suspect you have plague, you're likely to start by going to an emergency room. You may eventually need to see a doctor specializing in infectious disease.

What you can do

If you have respiratory symptoms, you may need to wear a surgical mask to your appointment to help prevent spreading the disease to others. You might also want to:

Write down any symptoms you're experiencing, including when they started.

Write down key personal information, including whether you've recently traveled to an area where plague is common and whether you've handled wild animals.

Make a list of all medications, vitamins or supplements you're taking.

Bring a family member or friend along, if possible. Sometimes it can be difficult to soak up all the information you get during an appointment. Someone who accompanies you may remember something that you missed or forgot.

Write down questions to ask your doctor.

For plague, some basic questions to ask your doctor include:

What is likely causing my symptoms or condition?

Other than the most likely cause, what are other possible causes for my symptoms or condition?

What tests do I need?

What is the best course of action?

Will I need to be in isolation?

What are the alternatives to the primary approach you're suggesting?

I have these other health conditions. How can I best manage them together?

Are there any restrictions I need to follow?

Don't hesitate to ask any other questions.

What to expect from your doctor

Your doctor is likely to ask you a number of questions, including:

When did you begin experiencing symptoms?

Have you recently traveled to areas where plague is common?

Have you recently handled wild animals or cats?

Are you aware of having been bitten by fleas?

Have your symptoms been continuous or occasional?

How severe are your symptoms?

What, if anything, seems to improve your symptoms?

What, if anything, appears to worsen your symptoms?

If your doctor suspects plague, he or she may look for the Yersinia pestis bacteria in samples taken from your:

Buboes. If you have the swollen lymph nodes (buboes) characteristic of bubonic plague, a fluid sample can be taken from them with a needle.

Blood. Yersinia pestis bacteria generally are present in your bloodstream only if you have septicemic plague.

Lungs. To check for pneumonic plague, your doctor will take sputum or fluid from your airways using endoscopy — a thin, flexible tube inserted through your nose or mouth and down your throat.

Medications

As soon as your doctor suspects that you have plague, you'll need to be admitted to an isolation room in a hospital. There, you'll receive powerful antibiotics, such as:

Gentamicin

Doxycycline (Vibramycin)

Ciprofloxacin (Cipro)

In addition, the Food and Drug Administration has approved another antibiotic, levofloxacin (Levaquin), for treatment of plague.

Although no effective vaccine is available, scientists are working to develop one. Antibiotics can help prevent infection if you're at risk of or have been exposed to plague. Take the following precautions if you live or spend time in regions where plague outbreaks occur:

Reprint Permissions

A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.org," "Mayo Clinic Healthy Living," and the triple-shield Mayo Clinic logo are trademarks of Mayo Foundation for Medical Education and Research.